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7.2. Modulation: making the sound change
We now have a sound we can change in various ways – we can alter its pitch, its waveform
and harmonics, its overall frequency spectrum, and its loudness. All we have to do is turn all
the knobs at once in just the right way, to create every note we want to play, right?
Fortunately, there are elements built into the synthesizer that we can set up to do all of this
for us automatically, by sending control voltages to each element in the signal path. We call
these changes modulation , and there are a few simple modulators that do most of our work.
7.2.1. The envelope generator
The envelope generator (or just envelope) is a control voltage that starts, changes, and then
stops, according to settings for several stages that it passes through.
The most common envelope type, as found on the VCA of the CS-80, is the ADSR:
The Attack is the time that the sound will take to reach its maximum volume once
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we start the envelope;
The Decay is the time that the sound will take to drop from its maximum volume
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to the Sustain level;
The Sustain is the volume level that the sound will reach when a key is held down
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long enough to get through the Attack and Sustain;
The Release is the time that the sound will take to drop back to silence once we
•
stop the envelope.
The CS-80's VCF envelope has an unusual envelope that has two additional parameters:
The Initial Level (IL) is the start level of the envelope relative to the frequency
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of the filter, and it's usually lower than the cutoff frequency. This produces
interesting behavior: after the Attack and decay, the envelope settles in at the
cutoff frequency (so it doesn't have a Sustain control), then drops back down to
the initial level during the release.
The Attack Level (AL) is the maximum level of the filter envelope; we need to
•
add this parameter to control the shape of the envelope relative to the cutoff
frequency.
Arturia - User Manual CS-80 V - The Basics of Subtractive Synthesis
ADSR envelope
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